I am writting a win32 program with VB.NET which need to get some values from Mathematica. I use the sample program in Mathematica and write the code like this:

Imports System
Imports Wolfram.NETLink

Public Class Form1
    Public kernel1 As IKernelLink 

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        kernel1 = MathLinkFactory.CreateKernelLink()
        kernel1.WaitAndDiscardAnswer()
    End Sub

    Public Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        kernel1.Evaluate("<< StringConvertTools.x")
        kernel1.WaitAndDiscardAnswer()
        MsgBox("the data has been loaded successful", MsgBoxStyle.OkOnly, "info")
    End Sub

    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        Dim flag1 As Integer
        kernel1.Evaluate("1+2")
        kernel1.WaitForAnswer()
        flag1 = kernel1.GetInteger()
        kernel1.Evaluate("XHexceldata[#,True]&/@" + rownumber)
    End Sub

End Class

I run the porgram, I will first click the button1, then I will click the button2. But when I click the button2, there will be an erro message "Error code: 3. MLGet out of sequence". I found that the erro is caused by the code flag1 = kernel1.GetInteger(). I don't know why it can not get the value of "Evaluate("1+2"). And I found that the value of flag1 is always 0. But the sample in the document of .NETLink API here is:

Imports System
Imports Wolfram.NETLink

Public Class SimpleLink

    Public Shared Sub Main(ByVal args As String())

        ' This launches the Mathematica kernel:
        Dim ml As IKernelLink = MathLinkFactory.CreateKernelLink()

        ' Discard the initial InputNamePacket the kernel will send when launched.
         ml.WaitAndDiscardAnswer()

        ' Now compute 2+2 in several different ways.

        ' The easiest way. Send the computation as a string and get the result in a single call:
        Dim result As String = ml.EvaluateToOutputForm("2+2", 0)
        Console.WriteLine("2 + 2 = " & result)

        ' Use Evaluate() instead of EvaluateToXXX() if you want to read the result
        ' as a native type instead of a string.
        ml.Evaluate("2+2")
        ml.WaitForAnswer()
        Dim intResult As Integer = ml.GetInteger()
        Console.WriteLine("2 + 2 = " & intResult)

        ' You can also get down to the metal by using methods from IMathLink:
        ml.PutFunction("EvaluatePacket", 1)
        ml.PutFunction("Plus", 2)
        ml.Put(2)
        ml.Put(2)
        ml.EndPacket()
        ml.WaitForAnswer()
        intResult = ml.GetInteger()
        Console.WriteLine("2 + 2 = " & intResult)

        'Always Close when done:
        ml.Close()
     End Sub

End Class

I don't know what's wrong with my code. Can U give me some advice ? Thanks!